As you point out, some spreading plants can be effectively eternally immortal. For examples, certain fungus colonies in PNW are genetically one and have estimated ages of many thousands of years based on their spread and some shrub (blueberry i believe it was) stands in Pa cover many acres and are estimated to have similar age.

Bulbs and corms and many tubers are very different. They generally consume the entire unit to produce a seasonal plant and then a new unit(s) is produced from axillary buds to store resources for the next season and thus they have no continued life of their selves.

I would surmise that without competition many perennials and such will expand indefinitely untill restricted by lack of resources or overcome by disease or other killing conditions

"IE lets take an iris for instance, it's a creeping rhizome.....so
theoretically if it was able to keep spreading wouldn't it "live"
forever?"

Theoretically, yes ;-)) That's why one often comes across bearded irises blooming their heads off at abandoned homesteads or overgrown/neglected gardens decades after their initial planting.

Having said that, plants do have a life expectancy that varies widely depending on the plant. Often with herbaceous plants and sometimes bulbs, what you are seeing years later is not the original plant but an offspring. Some are just better at producing following generations unobtrusively (like the iris) so it's difficult to determine what was original and what is the replacement. Bit easier to see with trees :-))

the problem is that many of our favorites .. are what i call foo foo plants chosen/bred for pretty flowers.. rather than vigor ...

many species plants... iris.. in your example.. grow just as you sust they should ... but they have lesser flowers ...

but then we go breeding them out to 6 inch flowers.. like the bearded ones ... with no thought to breeding out vigor to carry that load ...

hybrid T roses are much akin.. to foo foo flowers .. that lack vigor in many other aspects ...

ken

Generalizing out even more: as one old gardening saying goes, plants don't die, gardeners kill them.

But as per the entries above, there's a lot more to it than that.

To Ken's first point, more showy perennials, which cost more (in part because they are harder to produce) are normally routinely less vigorous and hardy (and shorter lived) than "the oldies". I take "the oldies" to be species (wild-types) and also those cultivars (from the species) which have survived so long that the cultivar names of individual plants have been forgotten. The latter have just proven their worth to generations of gardeners.

Another adage in gardening is that if you want to know where to plant a plant (re growing conditions) buy three, plant them in three different locations and the plant will tell you where you should have planted it.

It's obvious that very many perennials are lost because they are simply planted in the wrong location (too much/too little sun, too dry, poor drainage, etc, etc., etc.).

And as Gardengal mentions, plants of whatever kind simply have a certain life expectancy, just like everything living. I might live to be 80, my cat will not, and nor will a bulb. An oak tree could easily outlive me though, barring external harm.

Well, heres one I would like an explanation for. Back in the early nineties, we had 60" of snow that winter. About 4 times more than usual. I had tulips come up that spring that I couldn't even remember when I had planted them. And I still had a pretty good memory back then. How could they lay dormant all those years, maybe as much as 20 ?

Texas - Try this link:

http://pabook2.libraries.psu.edu/palitmap/Huckleberry.html

or better yet:

https://en.wikipedia.org/wiki/List_of_longest-living_organisms

Look in the clonal colonies part.